feat: add addRouteMiddleware test

[wattanx]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

I would like to add addRouteMiddleware as it was not tested.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[wattanx]

@danielroe
Is the following usage of defineNuxtRouteMiddleware acceptable?
We would like to consider not supporting it because we think it would be difficult to support it in Nuxt Bridge.
(Because it would have to be converted to Nuxt 2 middleware.)

const authMiddleware = defineNuxtRouteMiddleware((to, from) => {
  ...
});

export default defineNuxtPlugin((_nuxt) => {
  addRouteMiddleware('auth', authMiddleware, { global: true })
})

[danielroe]

I would be happy to add a note that this is not supported (if we can't) 👍

[wattanx]

Thanks!
I added documentation on defineNuxtRouteMiddleware and stated that it is not supported.
nuxt/nuxt#21718